1. Field of the Invention
This invention relates generally to the production of multi-gauge metal strips, and is concerned in particular with a method of producing such strips with one or more relatively thin web segments having width to thickness ratios greater than about 50 to 1.
2. Description of the Prior Art
Multi-gauge strips have been produced by a number of known methods, including for example continuous casting, continuous hot forging, continuous rolling, milling or machining, welding and extrusion.
A continuously cast product has a relatively rough surface and a low strength "as cast" crystal structure. Moreover, only one alloy can be continuously cast at a time, and then only at relatively slow speeds in the range of 8 to 60 inches per minute.
Continuous forging is also characterized by relatively low production speeds as well as poor accuracy, and the resulting products have relatively rough surfaces, making it necessary to resort to further machining in order to achieve desired surface finishes and tolerances.
Continuous rolling requires multiple roll passes, each having specially machined rolls. Intermediate annealing is usually required, and the resulting product in often plagued by non-uniform stresses which in turn result in distortions, e.g., twist and camber.
Milling or machining entails the cutting away or removal of metal, thereby producing considerable scrap. Production speeds are again relatively low, usually in the range of 4 to 8 feet per minute, this being due in large part to the necessity of avoiding excessive heat build up in the product as well as the cutters. The resulting product surface is also frequently mared by cutter striations.
Welding requires a high energy source to melt the metal and thereby cause fusion. Thickness variations are produced at the weld site, and the weld area is characterized by a relatively low strength as cast crystal structure. Moreover, the welds are subject to imperfections such as blow-holes and insufficient penetration. Welding rates rarely exceed 20 feet per minute, and insoluble material such as silver and nickel cannot be bonded by this technique.
Extrusion is limited to one metal or alloy at a time, and then only to those metals which have a low recrystallization temperature and a low modulus of elasticity, e.g., copper, silver and aluminum alloys. Metals which gaul e.g., nickel and the platinum group metals cannot be extruded.
Many of the foregoing difficulties are exacerbated as the width to thickness ratios of the thinnest sections of the desired end products increase. When this ratio exceeds about 50 to 1, it becomes virtually impossible to successfully produce an acceptable product on a commercial scale with any of the above-described conventional methods.
The production of composite strips by means of solid phase bonding is also known. However, difficulties stemming from differential rolling stresses and resulting curvature distortion have prevented this method from being employed successfully in the production of multi-gauge products with width to thickness ratios exceeding about 50 to 1.
A general objective of the present invention is to provide an improved method of producing a multi-gauge metal strip which avoids the above-described shortcomings and problems of the prior art.